The match also featured the long-awaited PSG debut of Spanish defender Sergio Ramos, while Neymar left the pitch sobbing in agony, stretchered off with an ankle injury.
Still in November, the result leaves PSG on 40 points, 14 clear of second-placed Nice, who lost 1-0 at home to struggling Metz on Saturday. Saint-Etienne took a surprise lead when Denis Bouanga beat the offside trap to fire a shot past Gianluigi Donnarumma on 23 minutes, a flag went up but a VAR review awarded the goal.
The hosts, languishing in the bottom two but on the back of two straight league wins, held their own against PSG, who appeared more affected by the freezing cold and gusting snow. All that changed with a red card.
There was no VAR to save the hosts on the stroke of half-time when back-tracking defender Timothee Kolodziejczak was sent off for a flailing challenge on Kylian Mbappe. PSG then levelled when Marquinhos scored with a towering header as Messi floated in the subsequent free-kick, sending in the sides level, but with the hosts hanging their heads. "At best that was too harsh," said Saint-Etienne coach Claude Puel. "It changed the match, we were leading and doing well."
The second half was one-way traffic with further goals coming from Angel Di Maria on 79 and centre-back Marquinhos with his second in time added on -- Messi again providing inch-perfect passes. But there was bad news for PSG late on as Neymar fell in full flight after treading on a defender's leg and twisting his ankle in a way that made his teammates wince. "That's life," Neymar said on Instagram. "I'll be back better and stronger."
The result sees Saint-Etienne slip to the foot of the table, behind Metz on goal difference.
Standout matches today